The present study investigated MR's auditory agnosia in various domains of sound from a higher-level cognitive perspective and a lower-level perceptual perspective. MR was found to exhibit environmental and music agnosia amidst preserved function in the verbal and speech prosody auditory domains. Peretz's cognitive level of explanation succeeds in capturing MR's full spectrum of auditory cognitive impairments. However, the dimensions along which MR's agnosias dissociate are not consistent with Peretz's proposed pattern of associative agnosias. Peretz attributes the common dissociation of music and environmental agnosia to isolated processing systems, while she accounts for the typical co-occurrence of musical agnosia and aprosodia by suggesting a common processing system. MR's pattern of agnosias does not support Peretz's notion of common or isolated modules in this way. Moreover, his anomalous patterns of deficits along the melodic dimension are not satisfactorily explained by Peretz's proposed distinct module for melodic representation.
The adoption of a perceptual processing approach traditionally applied in normal populations revealed the great explanatory power of a low-level account of MR's auditory agnosias. Explanations based on pitch perception provide an informative account of MR's musical illusions, musical and environmental agnosia for pitches/sounds of short temporal durations, and preserved speech prosody function. An auditory scene analysis perspective provides a possible explanation for MR's impaired processing for patterns of sounds occurring over a longer temporal window, despite preserved pitch pattern perception at this level. This level of explanation also provides insight on MR's environmental agnosia beyond the scope of a pitch perception account.
In conclusion, MR's perceptual deficits appear sufficient to explain his differential patterns of deficits across auditory domains without recourse to explanations based on specific cognitive modules and mechanisms. Rather than simply attributing higher-level dissociated or co-occurring agnosias to common or isolated processing systems, the study of auditory agnosia dissociations from a perceptual perspective helps to clarify the functional and neural architecture underlying auditory cognition. Although Peretz's taxonomy is vital for preliminary assessment purposes, an apperceptive approach affords a greater understanding in the neuropsychological study of auditory agnosias caused by brain damage.